Revert "git-clone.txt: remove the restriction on pushing from a shallow clone"

This reverts commit dacd2bcc41.

"It fails reliably without corrupting the receiving repository when
it should fail" may be better than the situation before the receiving
end was hardened recently, but the fact that sometimes the push does
not go through still remains.  It is better to advice the users that
they cannot push from a shallow repository as a limitation before
they decide to use (or not to use) a shallow clone.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-clone.txt

@@ -182,13 +182,11 @@ objects from the source repository into a pack in the cloned repository.
 --depth <depth>::
 	Create a 'shallow' clone with a history truncated to the
 	specified number of revisions.  A shallow repository has a
-	number of limitations (you cannot clone or fetch from it, nor
+	number of limitations (you cannot clone or fetch from
-	push into it), but is adequate if you are only interested in
+	it, nor push from nor into it), but is adequate if you
-	the recent history of a large project with a long history.
+	are only interested in the recent history of a large project
-+
+	with a long history, and would want to send in fixes
-Pushing from a shallow clone should be avoided if the git version on
+	as patches.
-the receiver end is older than v1.7.10, or any other git
-implementation that does not perform connectivity check.
 
 --[no-]single-branch::
 	Clone only the history leading to the tip of a single branch,